The invention relates to a stator for an electric motor, having an essentially hollow cylindrical stator stack that is provided with wire windings, and an end winding which adjoins the stator stack in an axial direction, wherein the stator stack has a number of slots and wherein a coolant line is inserted into the respective slot.
In an electric motor, electrical energy is transformed into mechanical energy. In particular, the force exerted by a magnetic field on the coil conductors through which current flows is converted into motion. Electric motors can also execute translational motion, but are typically embodied as rotational motors.
Such an electric motor for generating a rotational motion usually has a fixed stator and a rotating rotor. The magnetic field of the stator is generated by permanent magnets or by a metal part provided with coil windings, also known as a stator stack. The stator stack typically has the structure of a hollow cylinder and is wound with the magnet wires. The respective ends of the wire windings typically emerge on one or both axial sides of the stator stack and form a wire mesh there in each case, wherein said wire mesh is also known as an end winding.
A rotor is arranged within the stator and in most cases consists of a coil having an iron core, the so-called armature, which is rotatably mounted in the magnetic field of the stator. The rotational motion is produced by the repulsion and attraction of the magnetic fields of stator and rotor. In the case of a direct-current motor, the rotation of the rotor ensures that current is supplied to the correct windings by a commutator at all times in order to achieve a continuous dynamic effect and hence rotation. A commutator can be omitted in the case of other design formats, e.g. asynchronous motors using three-phase current or alternating current, wherein an asynchronous motor has a squirrel-cage winding in the rotor instead.
In recent years, owing to the increased environmental awareness and the shortage of natural resources, greater use is being made of the electric motor as a means of vehicle propulsion. Electric propulsion is in many ways superior to the internal combustion engine, e.g. in terms of the efficiency and the advantageous torque and performance characteristics of an electric motor. Moreover, the drive train is for the most part significantly easier to construct.
However, the limited range of electric vehicles is often disadvantageous, resulting from the comparatively limited amounts of energy which can currently be carried in energy stores such as accumulators according to the prior art. The problem therefore arises, particularly in the case of electric vehicles, of using the available energy as efficiently as possible, i.e. optimizing the efficiency of the vehicle.
This can be achieved e.g. by utilizing waste heat which would otherwise be discharged into the engine compartment and therefore lost. Casings for electric motors are therefore often cooled by a fluid which flows through them and can then supply the heat to various units for further use, e.g. the interior heating. The fluid is guided in corresponding coolant lines which are inserted or cast-in. The casing is often in direct contact with the stator stack in this case, such that the heat produced in the stator stack can be removed directly.
It is often disadvantageous in this context that, due to the temperature drop between stator stack and cooled casing during operation, very high stresses are produced as a result of the thermal expansion. These can result in unacceptable distortions in the stator stack or casing. Therefore coolant lines are also integrated directly into the stator stack in some cases, said stator stack being provided with corresponding slots into which the coolant lines are inserted.